1. Field of the Invention
The present invention relates to a toroidal type continuously variable transmission utilized as a transmission for, e.g., an automobile.
2. Related Background Art
There has been pursued the use of a toroidal type continuously variable transmission illustrated in FIGS. 2 and 3 as a transmission for an automobile. In this toroidal type continuously variable transmission, as disclosed in, e.g., Japanese Utility Model Laid-Open Application No. 62-71465, an input disk 2 is supported concentrically with an input shaft 1, and an output disk 4 is fixed to the end of an output shaft 3. A casing encases the toroidal type continuously variable transmission. A support bracket is provided on the inner surface of the casing or inwardly of this casing. The support bracket is provided with trunnions 5, 5 each swinging about a pivot disposed in a twist position with respect to the input shaft 1 and the output shaft 3 as well.
Each of the trunnions 5, 5 is composed of a metal material exhibiting a sufficient rigidity. The pivots are provided on the external surface at both ends thereof. Power rollers 7, 7 are rotatably supported on the peripheries of displacement shafts 6, 6 provided at the central parts of the respective trunnions 5. Each of the power rollers 7, 7 is interposed between the input and output disks 2, 4.
Inner surfaces 2a, 4a of the input and output disks 2, 4 are disposed in a face-to-face relationship and concaved in a circular arc in section, with the pivots being centered. Then, peripheral surfaces 7a, 7a of the power rollers 7, 7 are spherically convexed and come into contact with the inner surfaces 2a , 4a.
A loading cam type pressure unit 8 is interposed between the input shaft 1 and the input disk 2. This pressure unit 8 elastically thrusts the input disk 2 toward the output disk 4. The pressure unit 8 is constructed of a cam plate 9 rotating together with the input shaft 1 and a plurality (e.g., four pieces) of rollers 11, 11 held by a holder 10. A cam surface 12 concaved and convexed in the peripheral direction is formed on one surface (right surface in FIGS. 2 and 3) of the cam plate 9. Further, a similar cam surface 13 3) is formed on an external surface (left surface in FIGS. 2 and of the input disk 2. Then, the plurality of rollers 11, 11 are rotatable about the axes in the radial directions with the input shaft 1 being centered.
With rotations of the input shaft 1 constituting a part of the toroidal type continuously variable transmission described above, the cam plate 9 rotates. Then, a cam surface 12 presses a plurality of rollers 11, 11 against a cam surface 13 formed on the outer surface of the input disk 2. As a result, the input disk 2 is pressed against the plurality of power rollers 7, 7. Simultaneously, the input disk 2 rotates when the pair of cam surfaces 12, 13 engage with the plurality of rollers 11, 11. Then, the rotations of this input disk 2 are transmitted to the output disk 4 via the plurality of power rollers 7, 7. The output shaft 3 fixed to this output disk 4 is thereby rotated.
In the case of changing the ratio of revolutions between the input shaft 1 and the output shaft 3, when effecting at first a deceleration between the input shaft 1 and the output shaft 3, as illustrated in FIG. 2, the trunnions 5, 5 are swung about pivots. The displacement shafts 6, 6 are tilted so that the peripheral surfaces 7a, 7a of the power rollers 7, 7 are brought into contact with the closer-to-center part of the inner surface 2a of the input disk 2 and with the closer-to-outer-periphery part of the inner surface 4a of the output disk 4.
Reversely, when performing an acceleration, the trunnions 5, 5 are swung as shown in FIG. 3. The displacement shafts 6, 6 are tilted so that the peripheral surfaces 7a, 7a of the power rollers 7, 7 come into contact with the closer-to-outer-periphery part of the inner surface 2a of the input disk 2 and with the closer-to-center part of the inner surface 4a of the output disk 4.
Tilt angles of the displacement shafts 6, 6 are set intermediate between those shown in FIGS. 2 and 3, thereby obtaining an intermediate transmission gear ratio between the input shaft 1 and the output shaft 3.
Further, for enhancing the power transmittable by the toroidal type continuously variable transmission that is constructed and acts as described above, as disclosed in Japanese Patent Laid-Open Application No. 2-163549, the arrangement has hitherto been proposed, wherein a pair of toroidal type continuously transmissions shown in FIGS. 2 and 3 are disposed in tandem in the power transmitting direction. FIG. 4 illustrates a structure in which the pair of toroidal type continuously variable transmissions are disposed in tandem.
A needle bearing 22 is provided between the inner peripheral surface of one end (left end in FIG. 4) of a circular-tube torque transmission shaft 14 and the outer peripheral surface of the end of the input shaft 1. The torque transmission shaft 14 is disposed concentrically with the input shaft 1. The input shaft 1 and the torque transmission shaft 14 are rotatable independently of each other.
A pair of input disks 2, 2 spaced away from each other are provided on the periphery of the torque transmission shaft 14. Ball splines 15, 15 are formed between the inner peripheral edges of the input disks 2, 2 and an outer peripheral surfaces 14a of the torque transmission shaft 14. The input disks 2, 2 are so supported on the torque transmission shaft 14 as to be impossible of rotating about this torque transmission shaft 14 but shiftable in the axial directions (right-and-left directions in FIG. 4) of the torque transmission shaft 14. Further, inner surfaces 2a, 2a of the input disks 2, 2 are each concaved in a circular arc in section.
Moreover, a pair of output disks 4, 4 are so provided between the pair of input disks 2, 2 as to be rotatable about the torque transmission shaft 14 and shiftable in the axial directions thereof. Inner surfaces 4a, 4a (inner surfaces of the disks 2, 4 imply the side surfaces of the disks 2, 4 that are disposed in a face-to-face relationship with each other in this specification) are concaved in the circular arc in section.
A ring-like output gear 18 is provided between the output disks 4, 4. This output gear 18 is fixed to the outer peripheral surface of a mid-portion of a cylindrical sleeve 19. Then, this sleeve 19 is so supported on the outer peripheral surface of a mid-portion of the torque transmission shaft 14 as to be rotatable about the torque transmission shaft 14 and shiftable by a small quantity in the axial directions thereof. Further, the pair of output disks 4, 4 are spline-engaged with the outer peripheral surfaces of both ends of the sleeve 19.
The cam plate 9 is rotatably supported on one end of the torque transmission shaft 14 through a thrust ball bearing 16. This cam plate 9 is connected via a flange plate 17 to the input shaft 1 and thereby rotate integrally. Then, a plurality of rollers 11 rotatably held by a holder 10 are interposed between the cam surface 12 and the cam surface 13. The cam surface 12 is formed on the inner surface (right surface in FIG. 4) of the cam plate 9. The cam surface 13 is formed on the outer surface of one input disk 2 (left in FIG. 4). Constructed in this way is a pressure unit 8 for thrusting this one input disk 2 in such a direction as to get apart from the cam plate 9 in the axial direction of the torque transmission shaft 14.
Besides, a stopper 20 and a flat plate spring 21 are provided between the torque transmission shaft 14 and the other input disk 2 (right in FIG. 4) which does not face to the pressure unit 8. Constructed in this manner is a stopper means for restricting this input disk 2 from moving in such a direction as to get away from the pressure unit 8.
Furthermore, the trunnions 5 and the plurality of power rollers 7 are provided between the inner surfaces 2a, 2a of the pair of input disks 2, 2 and the inner surfaces 4a, 4a of the pair of output disks 4, 4. The trunnions are swung about the pivots existing in the twist positions with respect to the torque transmission shaft 14. The power rollers 7 have spherically concaved peripheral surfaces 7a and rotatably supported on the displacement shafts 6 retained by the trunnions 5. Then, the peripheral surfaces 7a of the power rollers 7 are brought into contact with the inner surfaces 2a, 4a of the input and output disks 2, 4 by dint of a pressing force of the pressure unit 8.
Based on the structure wherein the pair of toroidal type continuously variable transmissions constructed as mentioned above, a rotational torque inputted from the single input shaft 1 is transmitted to one input disk 2 via a flange plate 17, the cam plate 9 and the pressure unit 8. The input disk 2 rotates with the torque transmission shaft 14. Then, with the rotations of the torque transmission shaft 14, the other input disk 2 rotates in synchronization with one input disk 2.
The rotary motions of the pair of input disks 2, 2 rotating synchronously through the torque transmission shaft 14 are transmitted respectively via the plurality of power rollers 7 to the pair of output disks 4, 4. The sleeve 17 spline-engaged with the two output disks 4, 4 is thereby rotated. Subsequently, the rotary motion of this sleeve 19 is taken out by means of the output gear 18.
When incorporating the transmission into a front-engine rear drive vehicle, it is preferable that:
(1) the rear end of the crankshaft of the engine and the front end of the propeller shaft be located on substantially the same straight line; and PA1 (2) the components of the transmission be disposed substantially uniformly in the circumference of the straight line described above.
On the other hand, the pair of toroidal type continuously variable transmissions shown in FIG. 4 are disposed in tandem. In the case of this structure, it is impossible to, if left as it is, place the input shaft 1 connected to the crankshaft and the output shaft connected to the propeller shaft on the same straight line. Namely, a take-off shaft to which a gear meshing with the output gear is fixed inevitably deviates sideway from the line of extension of the input shaft 1 by a distance measured as a total of a radius of the output gear 18 and a radius of the above-mentioned gear. Consequently, if the take-off shaft is employed directly as an output shaft, it is impossible to locate the rear end of the crankshaft of the engine and the front end of the propeller shaft on the same straight line.
For this reason, as disclosed in Japanese Utility Model Publication No. 3-2041, the input shaft 1 and the output shaft are concentrically disposed. At the same time, the front end of this output shaft is connected via the gear to the rear end of the take-off shaft. More specifically, as illustrated in FIG. 5, two lengths of take-off shafts 23, 23 are disposed in parallel with the input shaft 1 in a side-by-side relationship. Simultaneously, gears 24, 24 fixed to the front ends of the take-off shafts 23, 23 mesh with the output gear 18.
On the other hand, gears 25, 25 fixed to the rear ends of the take-off shafts 23, 23 mesh with a gear 27 fixed to the front end of an output shaft 26. With the construction described above, the rotating force can be transmitted between the input shaft 1 and the output shaft 26 disposed concentrically with each other.
In the case of the structure shown in FIG. 5, however, the rear end of the transmission is provided with the transmission mechanism consisting of the gears 25, 27. Therefore, a weight of the rear end portion of the transmission inevitably increases. When mounting the transmission in the automobile, the front end of this transmission is connected to the rear end of the engine. Hence, the rear end of the transmission serves as a free end. If the weight of this rear end portion increases, however, the vibrations and noises tend to undesirably augment during an operation of the engine. Besides, in the structure illustrated in FIG. 5, it is difficult to make the centers of the input disks 2, 2 and the output disks 4, 4 coincident with the centers of the power rollers 7, 7. A sufficient transmission efficiency can not be necessarily obtained.
That is, the rollers 11, 11 thrust the outer surfaces of the output disks 4, 4 upon an operation of the transmission. At this moment, the input disk 2 and the output disk 4 that are provided on the left side in FIG. 5 slightly move to the left hand in the same Figure. As a result, the centers of curvatures of the inner surfaces 2a, 4a of the two disks 2, 4 deviate from the center of curvature of the power roller 7 the peripheral surface 7a of which comes into contact with the two inner surfaces 2a, 4a. This results in a deterioration in state of the contact between the surfaces 2a, 4a, 7a. This further worsens the efficiency of transmission between the input disk 2 and the output disk 4.
Further, it is required that the input disk 2 constituting the toroidal type continuously variable transmission be impossible of relative rotations about the shaft member which supports this input disk but be so supported as to be shiftable in the axial directions. For this purpose, female splines 25 are, as illustrated in FIG. 7, formed over the entire length of the inner peripheral surface of the input disk 2 incorporated into the conventional toroidal type continuously variable transmission shown in FIG. 4.
When the female splines 25 are, as described above, formed over the entire length of the inner peripheral surface of the input disk 2, the working does not particularly become troublesome. The costs for manufacturing the input disks do not therefore increase.
On the other hand, the present inventors have devised the toroidal type continuously variable transmission (see FIG. 1 showing an embodiment of this invention) for the purpose of restraining small the vibrations and noises caused when used. In the case of this transmission, as illustrated in FIG. 8, the female splines 25 are formed not over the entire inner peripheral surface of the input disk 2 but partly in the axis direction thereof. Besides, it is required that a minor diameter R of this female spline 25 be set larger a minor diameter r (R&gt;r) of the central hole 26 formed in the input disk 2.
The above-mentioned working of the input disk 2 shown in FIG. 8 is difficult. A problem expected is that the costs for manufacturing the input disks 2 augment if left as it is.